1) Combine vinegar, red wine, soy sauce, garlic and pepper in a zippered plastic freezer bag. Add boneless leg of lamb. Seal bag, pressing out any air and distribute marinade around lamb in bag. Place in refrigerator for 8 hours to overnight.
2) Preheat oven to 350 degrees. Remove lamb from marinade. Place fat side up on a rack in a roasting pan.
3) Roast until instant read thermometer registers 125 degrees, about 1 ½ hours (18 minutes per pound for medium rare) or until desired doneness. Roasting Times 350 degrees for about 1 ½ hours or 18 minutes per pound for rare, 125 degrees 20 minutes per pound for medium-rare, 130degrees 22 minutes for medium, 140 degrees Notes A thin layer of fat protects the lamb from drying out during the cooking process. Trim any excess fat before serving.